The receptor for GM-CSF is expressed in vivo on thymic DC1 precursors, which have lost the potential to generate T cells.

(A) Representative cell size (FS) and flow cytometry profile (shaded monoparametric histograms) of CD44^hi and CD44^lointermediate CD34^lo progenitors electronically gated (biparametric plots) on Lin⁻ freshly isolated thymocytes. Background fluorescence determined with isotype-matched irrelevant MoAbs is shown (unshaded histograms). (B) DC, NK cell, and T-cell precursor potential of CD44^lo (empty bars) and CD44^hi (filled bars) intermediate CD34^lo thymic progenitors sorted from freshly isolated Lin⁻ thymocytes as shown in (A), and reanalyzed as shown in the biparametric plot (left panel). Generation of DCs and NK cells per 10⁵ input progenitors was assessed as described in Figure 2 after 11 days of culture (middle panel). Generation of T cells was assessed in hu/moFTOC by day 19. Absolute numbers of cells of the indicated phenotypes recovered per thymic lobe after reconstitution with 2 × 10⁴ progenitors are shown (right panel).